Sounds like quite a project. Good Luck
Several thoughts on some of the mods you plan:
Lowering the suspension 2 inches can help handling and reduce aerodynamic drag. It can also produce tire and wheel bearing wear problems. Be careful how you apply this for street use.
You seem to be working in opposite directions at the same time regarding the aero changes and the desire for improving fuel economy. Improved downforce almost always means increased aero drag.
You may want to consider an aftermarket radiator to help with engine cooling. The original is durable but sensitive to reduced airflow. A racing type core may help there or adding an oil cooler. They made a difference when Team Highball ran the 626 in the RS challenge for the Johnson Brothers.